1. Field of the Invention
The present invention relates to a sine wave generation circuit and an uninterruptible power supply system (UPS) using the same, and more particularly to a sine wave generation circuit and an uninterruptible power supply system (UPS) using the same, which can output a sine wave for direct current (DC) power stored in a battery.
2. Description of the Related Art
All electronic products using commercial power receive sine waves in order to operate normally. Where an electronic product is implemented as a mobile electronic product or backup equipment, electric power corresponding to the commercial power must be provided to the electronic product. Mobile electronic products using commercial alternating current (AC) power include commercial laser and light equipment (100 W–500 W), measurement equipment (100 W–1 KW) installed in a special vehicle for performing various inspections, a bus-dedicated television or refrigerator (100 W–1 KW), etc. Furthermore, the backup equipment includes an uninterruptible power supply system (UPS) (500 W–3 KW), a frequency converter (500 W–1 KW), a solar-cell power converter (1 KW–5 KW), etc.
As described above, the mobile electronic product and backup equipment using the commercial AC power are commonly equipped with a battery, convert direct current (DC) power stored in the battery into the commercial AC power, and provide the commercial AC power to a load (or a main body of an electronic product).
However, an inverter (e.g., an AC-DC converter) provided in the mobile electronic product mostly outputs a modified square wave. Thus, the inverter can cause a serious damage to an electronic product equipped with a motor. In addition, the inverter is large and heavy.
Since a converter (e.g., a DC-DC converter) or inverter for use in the backup equipment uses an inductance and capacitance (LC) resonant circuit to generate an AC wave, the efficiency of the converter or inverter is very low. Furthermore, since the converter or inverter for use in the backup equipment is large and heavy, its mobility is limited and its price is high.
On the other hand, an accident due to a power failure frequently occurs recently in comparison with the past. The amount of damage due to the power failure at the present is more considerable in comparison with that at the past. The UPS is a system for supplying high-quality electric power to prevent an outage or malfunction of a facility due to a sudden power supply failure associated with an instantaneous power failure or an instantaneous voltage or frequency variation in highly advanced computers, plant monitoring control devices, communication equipment, plant process control devices, and major equipment for use in a hospital, etc. The UPS provides electric power during a power outage using a battery to prevent damage due to the above-described power failure, to prevent an undesired outage of industrial machines, and to eliminate the inconvenience in using the Internet and in daily life.
According to a structure of the UPS, the UPS includes a mechanical UPS and an electronic UPS. The mechanical UPS stores electric energy when electric power is supplied normally, rotates a motor with DC voltage stored in the battery at the time of a power failure, drives a generator with the rotating force, and produces commercial AC voltage. The electronic UPS consecutively converts the battery's voltage in a predetermined period to produce AC voltage.
In the case of the mechanical UPS, a waveform of the AC voltage must be identical to that of the commercial AC voltage. When a device receiving electric power is an inductive load, a motor brush can be damaged due to ark generation where the AC power supply cannot maintain a 60 Hz sine wave. If voltage induced through a transformer is inappropriately increased, a load device can be damaged. Furthermore, since the mechanical UPS is large and heavy and its efficiency is low, it is difficult for the mechanical UPS to be used in small-sized equipment or indoors.
In the case of the electronic UPS, its circuitry is complex. The electronic UPS is expensive and frequently failed because it must drive the circuit at a high speed. Accordingly, an improved method used by most UPSs cheaply produces a square wave, produces AC power (based on the square wave) through a linear transformer, removes values of starting and end points of the square wave using an inductance and capacitance (LC) resonant circuit, etc., and produces and uses a wave similar to a sine wave. Since this improved method cannot produce a true AC wave, a motor can be seriously damaged. The above-described electronic UPS has low efficiency and is large and heavy. Furthermore, the conventional UPSs cannot be applied to mobile products.
The conventional UPSs have been fixed in the past. However, the UPSs need to be carried to various locations since the electric power is used not only in industrial machines but also in daily life. To do this, the UPSs must be lightened in weight and slimmed in size. Of course, the UPSs must functionally supply a 60 Hz sine wave as in a commercial power supply.
FIG. 1 is a view illustrating an exemplary conventional uninterruptible power supply system (UPS).
A rectifying/charging unit 101 rectifies commercial alternating current (AC) power when the commercial AC power is supplied, converts the rectified commercial AC power into direct current (DC) power, and charges a battery 103 with the DC power.
An inverter 105 receives the DC power from the rectifying/charging unit 101 and the battery 103 connected to the rectifying/charging unit 101 in parallel. Furthermore, the inverter 105 generates AC power in the form of a square wave in response to a pulse width modulation (PWM) control signal from a PWM generator (not shown in FIG. 1).
A linear transformer 107 boosts a level of AC power applied from the inverter 105, and an inductance and capacitance (LC) resonant circuit 109 converts the AC power boosted by the linear transformer 107 into the form of a sine wave by removing peak values of starting and end points of a square wave.
For reference, circuits of the inverter 105 and the linear transformer 107 can be configured as shown in FIG. 7.
If the commercial AC power is appropriate, a bypass switch 111 applies the commercial AC power to a load. On the other hand, if the commercial AC power is inappropriate, auxiliary power processed by the system elements indicated by the reference numerals 101 to 109 is applied to the load.
As described in relation to FIG. 1, the conventional UPS configures a filter circuit such as an inductance and capacitance (LC) resonant circuit to generate a sine wave. The conventional UPS cannot correctly generate the sine wave. Thus, the efficiency of the conventional UPS is low. The conventional UPS is large in size and heavy in weight. Furthermore, the conventional UPS cannot be appropriately applied to a mobile product.
As the linear transformer 107 is employed when the DC power of the battery 103 is boosted, there are problems in that the efficiency of the conventional UPS is low, and the conventional UPS is large in size and heavy in weight.
On the other hand, a digital amplifier is an amplifier for digitally amplifying an analog source signal. After converting the analog source signal into a pulse width modulation (PWM) signal, the digital amplifier carries out an amplifying operation for the PWM signal. The PWM signal indicates a digital signal of one bit, and an audible signal level associated with the PWM signal is recorded as signal width. An amplifying stage for amplifying the PWM signal as a type of switch does not affect straight wave characteristics associated with a transistor. The PWM signal is filtered by a low-frequency filter, and is restored to an original analog signal. The digital amplifier or D-class amplifier restores the original analog signal using the low-frequency filter after amplifying a digital signal using the PWM amplifier.
Where the D-class amplifier is used, a desired output wave can be reproduced and outputted. Thus, where the D-class amplifier is applied to the mobile electronic product or backup equipment such as an electronic product using commercial AC power, DC power stored in the battery is converted into a waveform (or sine waveform) signal of high-quality commercial AC power, and the high-quality commercial AC power can be applied to a load.
The basic concept of the digital amplifier has been known since the 70's, but technology of the D-class amplifier was not applied to the field in the invention. The reason is that high fidelity performance of the digital amplifier can be implemented only when a digital signal processing (DSP) algorithm for converting a pulse code modulation (PCM) code into a PWM signal, technology for designing a high-speed DSP application specific integrated circuit (ASIC) operating at 100 MHz or above, and all technologies of electronic and information industrial fields for digitally switching and amplifying a low-power PWM signal to a high-power PWM signal are entirely harmonized. For this reason, no amplifier having the high fidelity performance has been commercialized up to now.